It is known in the prior art to prepare calcium silicates by the reaction of a reactive silica or clay by the addition of silica to a lime suspension in a batch reaction. Calcium silicates are also known to be absorbent materials. See for example U.S. Pat. Nos. 1,574,363 and 3,033,648.
U.S. Pat. No. 1,422,004 to Sherwin discloses a method of recovering sodium aluminate from aluminum containing ore, wherein the ore is reacted with lime at sintering temperatures. Lime and silica are reacted and calcined in the absence of sodium oxide and soluble aluminum in Endres U.S. Pat. No. 1,613,448.
U.S. Pat. No. 2,438,488 to Anderson et al is directed to a process for producing Portland cement wherein aluminum, calcium, sodium, and silica are reacted at sintering temperatures to form calcium alumino silicate intermediates. The intermediates have a CaO to SiO.sub.2 molar ratio of 1.9 to 2.0:1.
A pigment prepared by the reaction of an alkaline earth metal silicate and aluminum sulfate in an aqueous medium is disclosed in U.S. Pat. No. 2,786,758 to Taylor. The pigment, which is used in the production of paper, does not contain sodium.
U.S. Pat. No. 2,888,377 to Allen describes the reaction of calcium hydroxide and silica under superatmospheric conditions, in the absence of sodium or soluble aluminum, to produce crystalline calcium silicate pigments useful in the production of paper.
Hydrated calcium silicates formed by the hydrothermal reaction of lime and silica are also disclosed in U.S. Pat. No. 2,995,447 as anti-caking agents or dispersing agents in dried dairy products. According to this patent, the reaction between lime and silica is carried out in the presence of water at an elevated temperature. This product does not appear to contain any other component such as aluminum.
U.S. Pat. No. 3,238,052 to Burak discloses a process for the production of silicates by reaction of a reactive silica, lime, and alumina in an aqueous solution. There were several disadvantages to this process. The aluminum was derived from aluminum sulfate and aluminum alum, both of which contain SO.sub.4.
In the present invention, the presence of SO.sub.4 has been shown to cause a reduction in the oil absorption property of the resulting pigment. In addition, the silicate product does not contain Na.sub.2 O, which has been shown by the present invention to produce lower density and higher oil absorbing products.
U.S. Pat. No. 3,264,130 to Mays discloses a process for producing silicate pigments, and the pigments produced therefrom, wherein reactive silicas are reacted with alkaline earth metal hydroxides. While the reactive silicas used in this patent contain alumina, the alumino component is apparently not reactive. Further, Na.sub.2 O is not used in the reaction. The resulting pigment therefore has a lower oil absorption proportion than pigments produced from reactions wherein reactive alumina and Na.sub.2 O are present. Finally, the pigments of the patent are crystalline or polymorphous in nature. This patent is probably the basis for a product of this type sold by the J. M. Huber Corporation under the trademark NOPAK.RTM. in the 1960's.
U.S. Pat. No. 3,567,667 discloses mould lining compositions which comprise a ball mill dust and calcium silicate or calcium alumino silicate fibrous refractory material. In this patent the calcium silicate and calcium alumino silicate materials are described as being preferably slag wool or a material known as Eldorite.
U.S. Pat. No. 4,243,429 to Tamura et al describes a process for making the mineral tobermorite by reacting a lime and a siliceous material containing alumina in an alkali solution under hydrothermal conditions. The tobermorite has the formula: 5CaO:6SiO.sub.2 :5H.sub.2 O, and contains no Na.sub.2 O or Al.sub.2 O.sub.3. Additionally, ettringite, a calcium alumino sulfate, is produced.
The present invention provides an amorphous alkaline earth metal alumino silicate which has use as an absorbent material in many areas.